Isolate and characterize the selenium prosthetic group of glutathione peroxidase. Study unique properties of glutathione peroxidase - kinetic properties, reactive site, etc. Define pathways for biosynthesis of the prosthetic group of glutathione peroxidase. Study tissue distribution and properties of non-selenium-dependent glutathione peroxidase. Study the mechanism by which glutathione peroxidase provides protection to a sensitive enzyme, isocitrate dehydrogenase, against lipid hydroperoxide. Determine by breath analysis the effect of varying selenium levels in a vitamin E and selenium-deficient diet on the production by rats of the lipid peroxidation product, pentane. BIBLIOGRAPHIC REFERENCES: Chiu, D.T.Y., F.H. Stults and A.L. Tappel. Purification and properties of rat lung soluble glutathione peroxidase. Biochim. Biphys. Acta 445:558-566 (1976). Pierce, S. and A.L. Tappel. Effects of selenite and selenomethionine of glutathione peroxidase in the rat. J. Nutr. (1977), in press.